A spectator selects either of the two boards (no force), which is threaded on the ribbon. We will presume the red board is threaded on the ribbon. The ends of the ribbon are held securely by a spectator. The yellow board is in the performers hand. Both the boards are covered by a handkerchief for a few moments. (Handkerchief not shown in illustration above for clarity) When the handkerchief is removed, the boards are found to have changed places, with the yellow board now on the ribbon and the red board in the performer’s hand. And everything can be handed over for thorough examination.
This is a novel effect, easy to perform, with props you can carry in your pocket, and use for a reasonably large audienmce. We supply you the special mechanical boards (playing card size, approximately 60mm x 90mm size), with the ribbon and detailed instructions.